This invention relates to an image processing apparatus or a drawing processing apparatus and in particular to a drawing processing apparatus for clipping and filling a plurality of clip areas of any shapes.
A drawing processing apparatus in computer graphics (CG), desk-top publishing (DTP), or the like can perform either or both of clipping of producing partial display of input image data, text data, etc., and filling of coloring the inside of a predetermined area, as required.
In some clipping, only rectangular areas can be handled as graphic form clip areas and in some clipping, areas of any shapes can be handled. In the clipping of handling only rectangular areas as clip areas, generally all intersection points of a drawing element and a rectangular area of a clip area are found and the inside or outside is determined, then only the clip area is displayed. Techniques based on such clipping are disclosed in the Unexamined Japanese Patent Application Publication Nos. Hei 1-103784, Sho 63-245576, and Sho 63-198174.
On the other hand, when areas of any shapes are frequently clipped as in CG or DTP, the number of intersection points of a drawing element and a clip area extremely increases. Therefore, if the above-described clipping method is used, the time consumed for determining the inside or outside of the clip area becomes enormous and the time taken in the clipping increases. As disclosed in the Unexamined Japanese Patent Application Publication No. Hei 6-168339, when a line having thickness is drawn, it becomes a graphic form of a complicated outline shape involving graphic forms at the end points and the connection points, so that the clipping time furthermore grows.
Then, a method of using an edge list to perform clipping is disclosed in the Unexamined Japanese Patent Application Publication No. Hei 6-274643. The edge list is used, whereby intersection processing is simplified as processing for each scan line and clipping can be performed at high speed.
However, the clipping method using an edge list involves a first problem of taking time in merging the processing results and a second problem of 2-step and complicated processing because filling is performed on a display list and then clipping is performed.
Another clipping method of graphic forms with vectors is disclosed in the Unexamined Japanese Patent Application Publication No. Hei 4-282784. In this method, however, only cases where graphic forms and clip areas are provided in a one-to-one correspondence with each other are considered for clipping. Thus, to process a plurality of clip areas, it becomes necessary to merge the processing results on a page memory, etc.,; still much time is taken in the merging.